Error control method, medium access control (MAC) frame designing method, and terminal registration method in wireless communication system, and recording medium

ABSTRACT

The MAC frame in a wireless communication system includes a terminal ID allocated to each of multiple terminals. At least one connection ID is allocated to each terminal having the terminal ID, and sub-carrier allocation information is allocated to each connection having the connection ID. The sub-carrier allocation information includes a sub-carrier allocation status for each sub-carrier, and the number of allocated information bits for each sub-carrier. The sub-carrier allocation status and the number of allocated information bits for each sub-carrier can be allocated, by sub-carriers, to the sub-carrier allocation information using a same number of bits; or the information on the sub-carrier allocation status is first allocated to the sub-carrier allocation information and the number of allocated information bits for each sub-carrier is allocated.

CROSS REFERENCE TO RELATED APPLICATION

This application is based on Korea Patent Application No. 2002-80317filed on Dec. 16, 2002 in the Korean Intellectual Property Office, thecontent of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

(a) Field of the Invention

The present invention relates to a medium access control (MAC) frameconstitution method, and an error control method. More specifically, thepresent invention relates to a MAC frame constitution method in awireless communication system using orthogonal frequency divisionmultiple access (OFDMA) technology.

(b) Description of the Related Art

The services provided in the conventional wireless communication systemsare those defined in the IEEE 802.16 standard, such as a real-timepolling service, a non-real-time polling service, or best effort (BE)service. In the IEEE 802.16 standard, the same number of informationbits are used for every time and frequency allocated to one connectionin allocation of the time and frequency resources. In this case,sub-carriers of the same channel gain are allocated irrespective ofchannel characteristics, so it is impossible to adaptively cope with thechannel characteristics, resulting in a deterioration of the systemefficiency.

SUMMARY OF THE INVENTION

It is an advantage of the present invention to provide a MAC framestructure that adaptively allocates time and frequency resourcesaccording to the channel status.

To achieve the advantage of the present invention, both the sub-carrierallocation status and the information bit allocation number of eachsub-carrier are transferred as sub-carrier allocation information.

In one aspect of the present invention, there is provided a MAC framedesigning method that includes (a) allocating a corresponding connectionID to each terminal; and (b) assigning information on a sub-carrierallocation status for the connection ID and the number of allocatedinformation bits of each sub-carrier to the sub-carrier allocationinformation.

Here, the step (b) includes allocating the number of allocatedinformation bits of each sub-carrier in addition to the information onthe sub-carrier allocation status. Alternatively, the step (b) includesassigning the information on the sub-carrier allocation status and thenthe number of allocated information bits of each sub-carrier for theallocated sub-carriers; or assigning, by sub-carriers, both theinformation on the sub-carrier allocation status and the number ofallocated information bits.

In another aspect of the present invention, there is provided aregistration method for registering a terminal with an access pointusing a MAC frame in a wireless communication system. The MAC frame isdivided into a downlink sub-frame including a broadcast interval and afirst management connection interval, and an uplink sub-frame includingan access interval and a second management connection interval. Thebroadcast interval is used for transmitting downlink and uplink mapmessages. The registration method includes: (a) the access pointreceiving a ranging request message from the terminal using the accessinterval; (b) the access point sending ranging allocation information tothe terminal using the downlink and uplink map messages; (c) the accesspoint performing ranging through a ranging slot; (d) the access pointreceiving a registration request message from the terminal using thesecond management connection interval; and (e) the access point sendinginformation on whether to permit the registration to the terminal usingthe first management connection interval.

Preferably, the access point sends the uplink and downlink map messagesto the terminal using the broadcast interval before it receives theranging request message.

In the ranging process, the access point receives a ranging responsemessage from the terminal, sends the downlink and uplink map messagesincluding the allocated ranging slot to the terminal, receives theranging request message from the terminal through the allocated rangingslot, and sends the ranging response message to the terminal using thefirst management connection interval.

In addition, the access point receives a ranging slot request messagefrom the terminal using the second management connection interval,reallocates the ranging slot to the terminal, and sends the downlink anduplink map messages including information on the reallocated rangingslot. Subsequently, the access point receives a ranging request messagefrom the terminal using the reallocated ranging slot, and sends aranging response message using the first management connection interval.

In a third aspect of the present invention, there is provided arecording medium with a built-in program which implements a function ofdesigning a MAC frame to register a terminal with an access point in awireless communication system. The function includes: allocating anaccess interval to the MAC frame so as to enable the terminal to send aranging request message to the access point; allocating a broadcastinterval to the MAC frame so as to enable the access point to senddownlink and uplink map messages including allocated ranging informationto the terminal; allocating an uplink management connection interval tothe MAC frame so as to enable the terminal to send a registrationrequest message to the access point; and allocating a downlinkmanagement connection interval to the MAC frame so as to enable theterminal to send information on whether to permit the registration and aranging response message to the terminal.

In a fourth aspect of the present invention, there is provided an errorcontrol method which is done using a control connection between receiverand transmitter in a wireless communication system. The error controlmethod includes: (a) setting up a control connection between thereceiver and the transmitter; (b) the receiver checking a receptionstatus of MPDUs (MAC Protocol Data Units) by frames when traffic exists;(c) the receiver constituting an acknowledgement (ACK) message for datatransmission in a previous frame and sending it to the transmitter; and(d) disconnecting the control connection when the traffic ends.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate an embodiment of the invention,and, together with the description, serve to explain the principles ofthe invention:

FIG. 1 is a schematic diagram of a wireless communication systemaccording to an embodiment of the present invention;

FIG. 2 is a flow chart of an error control process performed at thereceiver according to an embodiment of the present invention;

FIG. 3 is a flow chart of an error control process performed at thetransmitter according to an embodiment of the present invention;

FIG. 4 is a flow chart of an OFDM feedback information transfer processaccording to an embodiment of the present invention;

FIG. 5 shows the channel gain of each sub-carrier measured at aplurality of terminals;

FIGS. 6, 7, and 8 are conceptual diagrams of time and frequency domainsin TDMA, FDMA, and OFDMA, respectively;

FIG. 9 shows a comparison of system efficiencies depending on the numberof users;

FIG. 10 is a schematic diagram of a MAC frame according to an embodimentof the present invention;

FIG. 11 a shows the result of channel gain estimation;

FIG. 11 b shows the number of allocated bits for each sub-carrier;

FIG. 12 is a structural diagram of a downlink/uplink map informationelement in a downlink/uplink map message transferred using a broadcastinterval in the frame structure according to the embodiment of thepresent invention;

FIGS. 13, 14, and 15 are schematic diagrams of the sub-carrierallocation information according to first, second, and third embodimentsof the present invention, respectively;

FIG. 16 is a flow chart of an initial ranging process according to anembodiment of the present invention;

FIG. 17 is a flow chart of a process for the terminals determiningpermission of registration from an access point according to anembodiment of the present invention; and

FIG. 18 is a flow chart of a ranging process during data communicationaccording to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following detailed description, only the preferred embodiment ofthe invention has been shown and described, simply by way ofillustration of the best mode contemplated by the inventor(s) ofcarrying out the invention. As will be realized, the invention iscapable of modification in various obvious respects, all withoutdeparting from the invention. Accordingly, the drawings and descriptionare to be regarded as illustrative in nature, and not restrictive.

FIG. 1 is a schematic diagram of a wireless communication systemaccording to an embodiment of the present invention.

The wireless communication system according to the embodiment of thepresent invention is, as shown in FIG. 1, a point-to-multipointcommunication system comprising an AP (Access Point) 100, and aplurality of terminals 200 in communication with the AP by OFDM signalscheme. The AP 100 is connected to an Ethernet or an external network300 and in wireless communication with the multiple terminals 200 on awireless channel 400. The multiple terminals 200 and the AP 100 shareone wireless channel 400, so data must be transmitted without acollision.

In the MAC (Medium Access Control) layer of this wireless communicationsystem, a connection set-up process for BE (Best Effort) service,real-time VBR (Variable Bit Rate) service, and non-real-time VBR serviceis required.

The representative traffic of the real-time VBR service is MPEG (MovingPicture Experts Group) video stream. To set up a connection for thereal-time VBR service, service parameters are used that include trafficparameters such as maximum data transfer rate, average data transferrate, or maximum allowable burst value; and QoS (Quality of Service)parameters such as maximum delay time, allowable jitter value, or dataloss rate. The representative traffic of the non-real-time VBR serviceis FTP (File Transfer Protocol). To set up a connection for thenon-real-time VBR service, service parameters are used that includetraffic parameters such as maximum data transfer rate, average datatransfer rate, or maximum allowable burst value; and QoS parameters suchas maximum delay time, or data loss rate. The scheduler of the AP 100allocates wireless resources adequately to the corresponding VBRconnection according to each service parameter value. The representativetraffic of the BE service is HTTP (HyperText Transfer Protocol), SMTP(Simple Mail Transfer Protocol), or the like. There is no serviceparameter for the BE service.

Considering the characteristic of each service, as for the BE service,of which the service parameter does not exist, a connection set-up isperformed previously when the terminals 200 perform an initialregistration with the AP 100. But, for the VBR service, an appropriateconnection set-up is necessary according to the service parametersconcerned.

Once a connection for the real-time or non-real-time VBR service is setup, the terminal 200 piggybacks its buffer status on the last data MPDU(MAC Protocol Data Unit) of the corresponding connection of every MACframe, so it can request the AP 100 for an amount of data to betransferred to the next frame. To change the service parameters of theconnection, the terminal 200 preferably negotiates with the AP 100 onthe resource allocation change using a management connection. Inresponse to the change request, the AP 100 transmits changed downlinkand uplink maps to the next frame using appropriate scheduling.According to circumstances, however, the AP 100 may accept only a partof the resource allocation change requested by the terminal 200.

In the AP registration process of the terminal 200, the AP 100 allocatesa connection ID for the BE service to the corresponding terminal 200.When the terminal 200 newly requests the BE service on the managementconnection, the AP 100 allocates wireless resources using the BEconnection ID of the terminal 200. Once the connection for the BEservice is set up, the terminal 200 piggybacks its buffer status on thelast data MPDU of the connection of every MAC frame, so it can requestthe AP 100 for an amount of data to be transferred to the next frame. Inresponse to the change request, the AP 100 transmits changed downlinkand uplink maps to the next frame using appropriate scheduling. But,according to circumstances, the AP 100 may accept only a part of theresource allocation change requested by the terminal 200. In addition,the AP 100 may not guarantee defined wireless resource allocation in thenext frame for the BE connection in case of shortage of the wirelessresources. The BE service is then provided using the connection ID forEB that is allocated one by one to every terminal 200.

For stable data transmission on the non-real-time VBR or BE connection,an error control function must be provided. The error control functionwill be described with reference to FIGS. 2 and 3.

FIG. 2 is a flow chart of an error control process performed at thereceiver according to an embodiment of the present invention, and FIG. 3is a flow chart of an error control process performed at the transmitteraccording to an embodiment of the present invention.

During a process of initialization or registration with a newsub-network, the terminal 200 enters a step of registering with thecorresponding AP 100. In the meantime, one management connectionidentified by a 10-bit connection ID is set up on the terminal 200 andthe AP 100. Once the management connection between the terminal 200 andthe AP 100 is set up, the AP 100 periodically allocates wirelessresources for management connection to the terminal 200 by a basic modeset in the MIB (Management Information Base). The terminal 200periodically reports the AP 100 of the management MPDU amount to betransferred, and the AP 100 appropriately allocates wireless resourcesfor management connection to the terminal 200 according to themanagement MPDU amount reported by the terminal 200. On the managementconnection, the terminal 200 can request the AP 100 for new connectionset-up, connection change, or disconnection.

The access information of channels for management connection isbroadcast using a broadcast message in the broadcast interval. Forstable data transmission on the management connection, the error controlfunction must be provided.

Next, the error control method performed at the receiver will bedescribed with reference to FIG. 2. Each control connection is set upfor non-real-time VBR, BE, and management connections to provide theerror control function (in step 21). The receiver determines whether ornot traffic is received (in step 22). If there is no traffic received,then the receiver determines whether or not the traffic is terminated(in step 25). If there is received traffic, then the receiver checks theMPDU reception status by frames (in step 23). The receiver constitutesan acknowledgement (ACK) message ACK MPDU for data transmission in theprevious frame and sends the ACK message ACK MPDU (in step 24). The ACKmessage has a payload field that represents the first and last sequencenumbers successfully received in succession among the MPDUs transmittedin the previous frame. Without data transmission in the previous frame,the receiver does not send the ACK message. The receiver checks whetheror not the traffic is terminated (in step 25). If the traffic isterminated, then the receiver disconnects the control connection (instep 26); otherwise, it rechecks the MPDU reception status (in step 23).

Next, the error control method performed at the transmitter will bedescribed with reference to FIG. 3. Each control connection is set upfor non-real-time VBR, BE, and management connections (in step 31). Thereceiver sends the ACK message ACK MPDU for data transmission in theprevious frame. Then, the transmitter determines whether or not the ACKmessage ACK MPDU is received (in step 32). If the ACK message ACK MPDUis not received yet, then the transmitter resends MPDUs (in step 36).Upon receiving the ACK message ACK MPDU, the transmitter analyzes thereceived ACK message ACK MPDU by frames (in step 33), and determineswhether to resend the MPDUs (in step 34).

As stated above, the payload field of the ACK message includesinformation on the first and last sequence numbers successfully receivedin succession among the MPDUs transmitted in the previous frame. Inparticular, when there are several ranges of the MPDUs successfullyreceived in succession, the payload field includes the sequence numbersof the MPDUs of the first range only. Among the MPDUs transferred in theprevious frame, those out of the range of the sequence numbers reportedon the control connection are retransmitted (in steps 35 and 36). If thefirst sequence number reported on the control connection is not thesequence number of the first MPDU transferred in the previous frame,then the transmitter resends all the MPDUs transferred in the previousframe. The transmitter resends the MPDUs and checks whether or not thetraffic ends (in step 37). If the traffic is terminated, then thetransmitter disconnects the control connection (in step 38); otherwise,it analyzes the ACK MPDU by frames a second time (in step 33).

The error control function described with reference to FIGS. 2 and 3must be performed continuously during the holding time of the connectionunder the error control.

Reference will now be made to FIG. 4 as to an OFDM feedback informationtransfer function performed at the terminal 200. FIG. 4 is a flow chartshowing an OFDM feedback information transfer process according to anembodiment of the present invention.

Each terminal 200 measures the signal-to-noise ratio (SNR) in the unitsof frame in regard to the transmission quality of each sub-carrier, soas to report the AP 100 of the downlink transmission quality bysub-carriers (in step 41). If the SNR of each sub-carrier is changedfrom the previous SNR measurement by at least 1 dB (in step 42), thenthe terminal 200 constitutes OFDM-FBCK MPDUs (in step 43), and sendsthem to the AP 100 (in step 44). Each terminal 200 can transmit at mostone OFDM-FBCK MPDU per frame.

In the embodiment of the present invention, the OFDM signaling method isadapted as a signal modulation method in designing the physical layerproviding the above-mentioned services. The OFDM signaling method iswidely used in high-speed data communication systems using communicationchannels having a limited frequency bandwidth, because it reduces adeterioration of performance caused by inter-symbol interference formulti-path fading channels and has a high frequency efficiency.

Next, the channel characteristics between one AP and multiple terminalswill be described with reference to FIGS. 5 to 9.

FIG. 5 shows channel gains for the respective sub-carriers as measuredat a plurality of terminals; FIGS. 6, 7, and 8 are conceptual diagramsof time and frequency domains in TDMA, FDMA, and OFDMA, respectively;and FIG. 9 shows a comparison of system efficiencies according to thenumber of users.

As in the embodiment of the present invention, when there are one AP 100and multiple terminals 200 and the channel characteristics are notchanged over time, the channel characteristics between the terminals 200and the AP 100 are different from one terminal to another. As shown inFIG. 5, for example, the channel gain of one OFDM sub-carrier is low atterminal 200 a, but high at other terminals 200 b, 200 c, and 200 d. Itis preferable in this case to allocate this sub-carrier to the terminals200 b, 200 c, and 200 d, and another sub-carrier of a higher channelgain to the terminal 200 a, thereby enhancing the system resourceefficiency. Namely, the channel environment of each terminal 200 ismeasured in allocation of sub-carrier channels such that the sub-carrierchannel having the highest channel gain in the aspect of each terminal200 is used for communication between the AP 100 and the correspondingterminal 200 so as to maximize the frequency resource efficiency. Amultiple access method that enables one AP 100 to communicate withmultiple terminals 200 using a same OFDM symbol interval is called OFDMA(OFDM Access), and the OFDMA method of allocating resources adaptivelyto the channel environment is called adaptive OFDMA

In the traditional TDMA (Time Division Multiple Access) and FDMA(Frequency Division Multiple Access) methods shown in FIGS. 6 and 7,respectively, time or frequency resources are fixedly allocated to theindividual users irrespective of the difference in the channel gain ofeach sub-carrier, so the channel capacity for an increased number ofusers is the same as that for a single user. Contrarily, in the OFDMAmethod that adaptively allocates sub-carrier channels as in theembodiment of the present invention, a sub-carrier channel having thehighest channel gain for each user is selected and allocated to thecorresponding user so as to enhance the channel capacity, as shown inFIG. 8.

In the case where there are four users in FIG. 9, the OFDMA method (g1)of adaptively allocating the modulation method of each sub-carrierchannel is in system efficiency by about 83% than the TDMA or FDMAmethod (g2) of uniformly allocating fixed time or frequency resources byusers, and by about 33% higher than the TDMA or FDMA method (g3) ofusing an adaptive modulation method.

The terminal 200 belonging to the wireless communication systemaccording to the embodiment of the present invention can maintainmultiple connections at the same time and allocate multiple sub-carriershaving an independent modulation method per connection. Expediently, itis assumed in the following description that all the terminals have nomore one connection.

Theoretically, the terminal 200 can estimate the number of informationbits modulated on each allocated sub-carrier channel only if it hasinformation on its allocated sub-carrier channel, the correspondingchannel gain, and the received information transfer rate. In this case,the channel gain of each sub-carrier is calculated at the AP 100 and ateach terminal 200 using an independent channel estimation process. TheAP 100 has only to send information on a list of sub-carrier channelsallocated to each terminal 200 and the information transfer rate to theterminal 200, so it can reduce channel dissipation.

Now, a description will be given as to a MAC frame for transferring onlyinformation on a list of sub-carrier channels and the informationtransfer rate with reference to FIGS. 10 to 15.

FIG. 10 is a schematic diagram of a MAC frame according to an embodimentof the present invention; FIG. 11 a shows the result of channel gainestimation; and FIG. 11 b shows the number of allocated bits bysub-carriers.

One MAC frame 500 of the wireless communication system according to theembodiment of the present invention is, as shown in FIG. 10, temporallydivided into a downlink sub-frame 510 and an uplink sub-frame 520. Thedownlink is a channel for signal transmission from AP 100 to eachterminal 200, and the uplink is a channel for signal transmission fromeach terminal 200 to AP 100. The time division duplexing method is usedfor distributing uplink and downlink channels. The downlink sub-frame510 is divided into, according to function, a broadcast interval 511,and a downlink data, management, and control connection interval 513.The uplink sub-frame 520 is divided into, according to function, anaccess interval 521, and an uplink data, management, and controlconnection interval 522. These intervals 511, 512, 521, and 522 have avariable length. The slot is defined as a multiple of the OFDM symbol.These intervals 511, 512, 521 and 522 may be composed of a slot having adifferent length. The access interval 521 is an interval used for theterminals 200 trying to get a first access to the AP 100, and also for acontention interval possibly having a collision among the terminals 200.The broadcast interval 511 carries a preamble, a DD message, a UDmessage, a downlink map message, or an uplink map message.

In the adaptive OFDMA method, the channel gain estimation valuecalculated at the AP 100 must be matched to that calculated at theindividual terminals 200 in order to correctly estimate the number ofallocated information bits for each sub-carrier. Actually, the channelgain estimation values are unmatched, in which case the information bitallocation pattern by sub-carriers is changed even with small errorestimation. When the transmitter differs from the receiver in theanalysis result of the information bit allocation pattern for eachsub-carrier, the transport bit information allocated to the sub-carrierchannels with allocation errors are all missed which causes seriousdeterioration of the whole performance.

FIGS. 11 a and 11 b show the result of a simulation for channel gainestimation at a frequency-selective fading channel having a SNR of 10dB: FIG. 11 a presents the result of channel gain estimation in the 49thand 50th frames for a same channel; and FIG. 11 b presents the estimatednumber of bits allocated to each received sub-carrier based on theresult of the channel gain estimation of FIG. 11 a. It can be seen fromFIG. 11 b that even a small difference of channel gain estimation leadsto a considerable error in the calculation of the number of allocatedbits.

Next, a method for reducing estimation error in calculating the numberof allocated bits will be described in detail with reference to FIG. 12.

FIG. 12 is a structural diagram of a downlink/uplink map informationelement of a downlink/uplink map message transferred in the broadcastinterval in the frame structure according to the embodiment of thepresent invention.

The downlink/uplink map information element 600 according to theembodiment of the present invention comprises, as shown in FIG. 12, aterminal ID field 610, a terminal offset field 620, a connection IDfield 630, a repeating bit field 640, an uplink/downlink characteristicfield 650, a start slot field 660, an end slot field 670, a physicallayer type field 680, and a sub-carrier allocation information field690.

The terminal ID field 610 enables every terminal 200 connected to the AP100 to check whether or not the map information corresponds to itself.The terminal ID is allocated to each terminal from the AP 100 during theinitial registration process. If the terminal ID field 610 is matched toits terminal ID, then the terminal 200 processes map information fromthe terminal ID to a value just before the value represented by theterminal offset field 620. It the terminal ID field 610 is unmatched toits terminal ID, then the terminal 200 skips as much of the mapinformation as the value represented by the terminal offset field 620and checks the value of the terminal ID field 610. The terminal 200repeats this procedure until the terminal ID field 610 is matched to itsterminal ID.

As described above, each terminal 200 capable of maintaining multipleconnections at the same time may have multiple connections in aninterval defined by the terminal ID field 610 and terminal offset field620. The connection ID field 630, the repeating bit field 640, theuplink/downlink characteristic field 640, the start slot field 660, theend slot field 670, the physical layer type field 680, and thesub-carrier allocation information field 690 are allocated to eachconnection. The connection ID field 630, the repeating bit field 640,the uplink/downlink characteristic field 650, the start slot field 660,the end slot field 670, and the physical layer type field 680 have afixed length, but the sub-carrier allocation information field 690 has avariable length.

The connection ID field 630 represents a connection ID unique to everyterminal 200 connected to the network. Connection ID 0 is reserved forthe AP 100 and is used in the initial registration process. Therepeating bit field 640 provides information on whether or not the valueof the sub-carrier allocation information field 690 of the correspondingconnection is identical to that of the sub-carrier allocationinformation field 690 of the previous connection. For example, when thevalue of the sub-carrier allocation information field 690 of theconnection is identical to that of the sub-carrier allocationinformation field 690 of the previous connection, the repeating bitfield 640 is set to 1 and the sub-carrier allocation information field690 in the corresponding connection is not added. This preventsunnecessary allocation of the repeated sub-carrier allocationinformation 690 to minimize band dissipation.

The uplink/downlink characteristic field 650 is a code fordiscriminating a set of formulated physical layer parameters of thedownlink/uplink. The start and end slot fields 660 and 670 represent thepositions of the start and end slots of each connection, respectively.The physical layer type field 680 represents the type of the physicallayer operated by the system. The sub-carrier allocation informationfield 690 includes allocated sub-carrier information for each connectionand the number of allocated information bits for each sub-carrier.

Next, a description will be given as to a method for transferring thenumber of allocated information bits for each sub-carrier to theterminal or the connection by using the sub-carrier allocationinformation field 690 with reference to FIGS. 13, 14, and 15.

FIGS. 13, 14, and 15 are schematic diagrams showing the structure of thesub-carrier allocation information according to first, second, and thirdembodiments of the present invention.

In the sub-carrier allocation information structure 690 according to thefirst embodiment of the present invention, as shown in FIG. 13,information on whether or not a sub-carrier is currently allocated, andthe number of allocated information bits for each sub-carrier aretransmitted to every terminal or connection with a same number of bits.FIG. 13 shows, for example, the case where the number of sub-carriersper OFDM symbol is 96 and two bits are allocated for transmitting themaximum number of allocated information bits per sub-carrier. If the2-bit information allocated to each sub-carrier is 00 in this case, thenno information bit is allocated; if the 2-bit information is 01, then 2information bits are allocated; if the 2-bit information is 10, then 4information bits are allocated; and if the 2-bit information is 11, then6 information bits are allocated.

In this manner, the field representing the number of allocatedinformation bits of a predetermined size is assigned to all thesub-carriers, thus facilitating implementation, in the first embodimentof the present invention. Although the number of allocated informationbits is added even for the sub-carriers not allocated to thecorresponding terminal or connection in the first embodiment of thepresent invention, it may not be added for the sub-carriers notallocated to the terminal or connection. The embodiment of this patternwill now be described with reference to FIG. 14 as follows.

In the sub-carrier allocation information structure 690 according to thesecond embodiment of the present invention, as shown in FIG. 14,information 691 on whether or not a sub-carrier is allocated is firsttransferred to each terminal or connection, and information 692 on thenumber of allocated information bits is then additionally transferred tothe allocated sub-carriers only. FIG. 14 shows, for example, the casewhere the number of sub-carriers per OFDM symbol is 96 and two bits areused to represent the maximum number of allocated information bits persub-carrier. One bit is allocated to transmit information on whether ornot each sub-carrier is allocated, and the fields representing thenumber of allocated information bits are then added for the allocatedsub-carriers only. Namely, the fields representing the number ofallocated information bits are added for the first, third, . . . , 91stand 93rd sub-carriers having a sub-carrier allocation status value of 1.The values of these fields are 01, 10, . . . , 11 and 01, respectively.For example, the field values of 01, 10 and 11 represent 2-, 4- and6-bit information bit allocations, respectively.

In the second embodiment of the present invention, the fieldsrepresenting the number of allocated information bits are added for onlythe sub-carriers allocated to the terminal or connection to minimizechannel dissipation. But, in the second embodiment of the presentinvention, the corresponding terminal or connection is required tomemorize the positions of the sub-carriers allocated to it and map thenumber of allocated information bits later. Next, a description will begiven as to an embodiment for transferring information on whether or noteach sub-carrier is allocated, in addition to the number of allocatedinformation bits with reference to FIG. 15.

In the sub-carrier allocation information structure 690 according to thethird embodiment of the present invention, as shown in FIG. 15,information on whether or not the sub-carrier is allocated, and thenumber of allocated information bits are transferred at the same time toeach terminal or connection. FIG. 15 shows, for example, the case wherethe number of sub-carriers per OFDM symbol is 96 and two bits are usedto represent the maximum number of allocated information bits persub-carrier. When the information on whether the sub-carrier isallocated has a value of 1 (i.e., the sub-carrier is allocated),information on the number of allocated information bits for thesub-carrier is added. The information on the number of allocatedinformation bits can be 2-bit information of 01, 10 or 11 as in theexamples of FIGS. 13 and 14. In FIG. 5, the information representing thenumber of allocated information bits that has a value of 01, 10, . . . ,11 or 01 is added to the first, third, . . . , 91st, or 93rd sub-carrierof which the allocation status value is 1.

In the third embodiment of the present invention, whether or not thesub-carrier is allocated is checked in the order of sub-carriers so asto add information on the number of allocated information bits for theallocated sub-carriers only. This reduces channel dissipation, andfacilitates implementation in hardware, because the terminal orconnection can immediately acquire information on the number ofallocated information bits.

A comparison of the first, second, and third embodiments of the presentinvention in the aspect of channel dissipation reveals that thetransferring method of the first embodiment shown in FIG. 13 has lesschannel dissipation with a statistically small number of terminals orconnections for transferring resource allocation information everyframe, and that the transferring methods of the second and thirdembodiments shown in FIGS. 14 and 15 have less channel dissipation witha statistically large number of terminals or connections fortransferring resource allocation information every frame.

Next, reference will be made to FIGS. 16 and 17 in regard to an initialregistration process for the terminal 200 registering with the AP 100.

FIG. 16 is a flow chart of an initial ranging process according to anembodiment of the present invention, and FIG. 17 is a flow chart of aprocess for the AP 100 determining whether to permit the registration ofthe terminal 200 according to an embodiment of the present invention.

The initial registration process of the terminal 200 with the AP 100comprises an initial ranging process of FIG. 16, and a process of the AP100 determining whether to permit the registration of the terminal 200as shown in FIG. 17.

The initial ranging process is a process in which the terminal 200 to beconnected to the network for the first time communicates information ontime synchronization, power level, or frequency offsets with the AP 100prior to a permission of the AP 100. As illustrated in FIG. 16, theterminal 200 receives a downlink/uplink map message from the AP 100 (instep 61), and sends a ranging request RNG-REQ message at an accessinterval to the AP 100 (in step 62), to perform first ranging. In thismanner, the first ranging is done through a contention using the accessinterval, and if it is done successfully, the AP 100 allocates a rangingslot to the terminal 200 (in step 63).

Subsequently, the AP 100 sends a ranging response RNG-RSP message to theterminal 200 using a specific connection ID (in step 64), and then adownlink/uplink map message to the terminal 200 (in step 65). Thedownlink/uplink map message includes allocation information on theranging slot allocated by the AP 100. Upon receiving the downlink/uplinkmap message, the terminal 200 sends the ranging request RNG-REQ messageto the AP 100 through a ranging slot (in step 66), and receives theranging response RNG-RSP message from the AP 100 through a managementconnection (in step 67). In this manner, the second ranging is performedusing the ranging slot to complete the initial ranging process.

After the completion of the initial ranging process, as illustrated inFIG. 17, the terminal 200 sends a registration request REG-REQ messageto the AP 100 on the management connection (in step 71). Theregistration request REG-REQ message includes information such asauthentication, transmission rate, capability, etc. The AP 100determines whether or not it can support the information such asauthentication, transmission rate, or capability as included in theregistration request REG-REQ message (in step 72). Then the AP 100 sendsa registration response REG-RSP message on the management connection toinform the terminal 200 of whether to permit the registration (in step73). If the registration result is confirmed as successful (in step 74),then the initial registration process ends (in step 75).

Next, a description will be given as to a ranging process when theterminal 200 connected to the network requests ranging a second timeduring data communication with reference to FIG. 18.

FIG. 18 shows, in a flow chart form, a ranging process during datacommunication according to an embodiment of the present invention.

The terminal 200 may decide to perform the ranging process a second timewhen the packet reception rate is deteriorated for a defined time perioddue to a change of the channel status. In this case, the terminal 200sends a ranging slot request (RNGSlot-REQ) message to the AP 100 on themanagement connection (in step 81), and the AP 100 allocates a rangingslot to the terminal 200 (in step 82). Following the allocation of theranging slot, the AP 100 sends a downlink/uplink map message includinginformation on the ranging slot allocation status to the terminal 200(in step 83). The terminal 200 sends a ranging request (RNG-REQ) messageto the AP 100 through the ranging slot (in step 84) and receives aranging response (RNG-RSP) message on the management connection (in step85), thereby completing the ranging process during data communication.

The above-described MAC frame designing method can be implemented as aprogram and stored in a recording medium such as CD-ROM, RAM, floppydisk, hard disk, magneto-optical disc, or the like. The MAC framedesigning method stored in the recording medium can be executed with acomputer.

While this invention has been described in connection with what ispresently considered to be the most practical and preferred embodiment,it is to be understood that the invention is not limited to thedisclosed embodiments, but, on the contrary, is intended to covervarious modifications and equivalent arrangements included within thespirit and scope of the appended claims.

The MAC frame structure of the present invention enables efficientprovision of a BE service, a real-time VBR service, and a non-real-timeVBR service, and maximization of efficiency of time and frequencyresources.

1. An error control method, using a control connection between areceiver and a transmitter in a wireless communication system, the errorcontrol method comprising: (a) setting up a control connection betweenthe receiver and the transmitter; (b) checking a reception status ofMPDUs (MAC (Medium Access Control) Protocol Data Units) by frames whentraffic exists; (c) creating an acknowledgement (ACK) message for datatransmission in a previous frame and sending it to the transmitter; and(d) disconnecting the control connection when the traffic ends, whereinthe ACK message includes a payload field representing the first and lastsequence numbers successfully received in succession among the MPDUstransmitted in the previous frame.
 2. The error control method asclaimed in claim 1, wherein the step (c) further comprises: analyzingthe ACK message and determining whether to resend the MPDUs.
 3. Theerror control method as claimed in claim 1, wherein the step (c) furthercomprises: analyzing the ACK message; and resending MPDUs other than therange of the sequence numbers reported through the payload field of theACK message.